Presentation Transcript

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Introduction :

“Nucleus” is a Latin word meaning Kernel
It is the “CONTROL CENTER” of the cell
It was First cell organelle to be discovered
It is membrane bound organelle found in eukaryotic cells
Main functions are
- to maintain the integrity of genes
- to control the activities of the cell by regulating gene expression Introduction 3 Nucleus

Historical Perspective :

Microscopist Antonie van Leeuwenhoek (1632 - 1723) observed a "Lumen", the nucleus, in the red blood cells of salmon
Mentioned by Franz Bauer in 1804
Scottish botanist Robert Brown elaborately described the nucleus studying orchids in 1831
In 1838 Matthias Schleiden proposed that the nucleus plays role in generating cells and introduced the name "Cytoblast" (cell builder) Historical Perspective 4 Nucleus

Nuclear envelope :

Also known as perinuclear envelope, nuclear membrane or karyotheca
Encloses the nucleus and separates the cell's genetic material from the surrounding cytoplasm
It is a lipid bilayer
Consists two cellular membranes, an inner & outer membrane, arranged parallel to one another and separated by 10-50(nm) of space Nuclear envelope 6 Nucleus

Nuclear pores and complex :

Nuclear pores are aqueous channels through the nuclear envelope
Composed of multiple proteins called nucleoporins”
Have molecular weight of 125 million daltons
Nucleus of a cell has 3000 - 4000 pores
Pores are formed by fusion of outer and inner nuclear membranes
NPC permits passive movement across the nuclear envelope via 9-11nm channels by simple diffusion Nuclear pores and complex 14 Nucleus

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Nucleus 15 Allows free passage of water soluble molecules
Most proteins, ribosomal subunits and RNA are transported via transport factors called KARYOPHERINS
a) Importins –that mediate movement into the nucleus
b) Exportins –that mediate movement out of nucleus
NPC is composed of nearly 100 proteins, arranged in eight-fold symmetry around the margin of the pore.

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Chromosomes :

It is an organized structure of DNA
Containing genetic information of cell, regulatory elements and other nucleotide sequences
Chromatin is a complex of DNA and histone protein, which packages chromosomes also known as nucleosomes
The structure of chromosomes and chromatin varies throughout the cell cycle
Interphase chromatin consists of euchromatin and heterochromatin (chromosomes are not visible during this phase) Chromosomes 18 Nucleus

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Euchromatin – contains active form of DNA
Heterochromatin - contains inactive form
Metaphase chromatin- the chromatin becomes more and more condensed and compact, making the chromosome visible with a classic four arm structure, having a pair of sister chromatids attached at centromere
Humans have 23 pairs of chromosomes- 22 are autosomes & 2 sex chromosomes 19 Nucleus

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Anti Nuclear Antibodies (ANA)
Antibodies to certain chromatin organizations, particularly nucleosomes, have been associated with a number of AUTOIMMUNE DISEASEAS such as
sytemic lupus erythematosus
systemic sclerosis/ scleroderma 21 Nucleus

Nucleolus :

Nucleolus is the discrete densely stained structure found in nucleus
It is a nuclear inclusion that is not surrounded by a membrane
Present in cells that are actively synthesizing proteins
Its size depends on metabolic activity of cell
Average size .5-5um in dia Nucleolus 22 Nucleus

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It is generally detectable when the cell is in interphase
Synthesis of rRNA and its assembly into ribosome precursors- main function
More than one nucleolus can be present in the nucleus 3nucleoli , nucleus of the spinosum cell layer of skin 23 Nucleus

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Nucleoplasm :

Nucleoplasm is the protoplasm within the nuclear envelope
It consists of a nuclear matrix and various types of particles
Highly viscous liquid which scaffolds chromosomes, nucleolus and various granules like heterochromatin, perichromatin granules
Many substances like nucleotides and certain enzymes are also dissolved in it Nucleoplasm 26 Nucleus

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Anucleated cells- which contain no nuclei, thus has no capacity to divide eg.
RBC Platelets
Polynucleated cells- With multiple nuclei eg.
Species of protozoa
Some fungi
Intestinal parasites like giardia
Giant cells in inflammation 30 Nucleus

Abnormal nuclear changes :

Nucleus 31 Abnormal nuclear changes

Functions :

Gene Expression- it involves replication & transcription (using DNA template to produce RNA)
This RNA produced is pre-mRNA which then needs to be translated to ribosomes to form proteins. This mRNA is transported out via nuclear pores in a facilitated transport
Cell compartmentalisation- nuclear envelope allows the nucleus to control its contents, and separate them from the rest of the cytoplasm where necessary Functions 32 Nucleus

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Where a cytoplasmic process needs to be restricted, a key participant is removed to the nucleus, where it interacts with transcription factors to downregulate the production of certain enzymes as in the pathway of glycolysis
Prevents translation of unspliced mRNA
Post Transcriptional Modification- newly synthesized pre-mRNA undergoes certain modifications before transported out to ribosomes in order to avoid its degradation. These are 5 capping, 3’polyadenylation and RNA splicing. Splicing involves removal of introns 33 Nucleus

Conclusively cell nucleus is the storehouse of everything what a cell shall do in future, since it handles the gene expression and overall metabolism of cellthus called “DIRECTOR OF CELL” :

Conclusively cell nucleus is the storehouse of everything what a cell shall do in future, since it handles the gene expression and overall metabolism of cellthus called “DIRECTOR OF CELL” 34 Nucleus